U.S. patent number 4,314,905 [Application Number 06/143,663] was granted by the patent office on 1982-02-09 for columnar fine mesh magnetized ion exchange resin system.
This patent grant is currently assigned to Purdue Research Foundation. Invention is credited to James E. Etzel, Anthony M. Wachinski.
United States Patent |
4,314,905 |
Etzel , et al. |
February 9, 1982 |
Columnar fine mesh magnetized ion exchange resin system
Abstract
A method and apparatus for water softening using less than
approximately 20 micron diameter fine mesh magnetized ion exchange
particles in columnar operation. The particles are formed by
encapsulating a core of magnetic material in ion exchange resin.
The particles are magnetized and disposed in a column where they
attach to magnetic mesh retention means such as stainless steel
wool. The design of the column permits use of the fine mesh ion
exchange particles and their properties of rapid exchange rates and
efficient utilization of resin capacity while avoiding prior art
problems of plugging, fouling, and excessive pressure drop.
Inventors: |
Etzel; James E. (Lafayette,
IN), Wachinski; Anthony M. (Panama City, FL) |
Assignee: |
Purdue Research Foundation
(Lafayette, IN)
|
Family
ID: |
26841283 |
Appl.
No.: |
06/143,663 |
Filed: |
April 25, 1980 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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957182 |
Nov 2, 1978 |
|
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|
Current U.S.
Class: |
210/670; 210/269;
210/687; 210/223; 210/679 |
Current CPC
Class: |
C22B
3/42 (20130101); B01J 20/3282 (20130101); B01J
39/17 (20170101); B01J 20/3293 (20130101); B01J
20/3425 (20130101); B01J 20/3475 (20130101); B01J
20/3276 (20130101); B01J 20/28016 (20130101); B01J
47/018 (20170101); B01J 47/02 (20130101); B01J
20/28026 (20130101); B01J 20/3204 (20130101); B01J
20/04 (20130101); B01J 20/28009 (20130101); B01J
20/28004 (20130101); B01J 20/0229 (20130101); B01J
2220/58 (20130101); Y02P 10/20 (20151101); B01J
2220/56 (20130101); Y02P 10/234 (20151101) |
Current International
Class: |
B01J
47/02 (20060101); B01J 20/32 (20060101); B01J
20/28 (20060101); B01J 39/00 (20060101); B01J
39/16 (20060101); B01J 20/30 (20060101); B01J
47/00 (20060101); B01J 049/00 () |
Field of
Search: |
;210/222,491,496,680,223,266,506,670,679,687,269 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Bashore; S. Leon
Assistant Examiner: Lander; Ferris H.
Attorney, Agent or Firm: Biebel, French & Nauman
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of application Ser. No. 957,182,
filed Nov. 2, 1978, now abandoned.
Claims
What is claimed is:
1. Apparatus for the ion exchange treatment of liquids with
fixed-bed ion exchange resins comprising:
a hollow column with an inlet and an outlet;
magnetic mesh retention means disposed in said column so as to
loosely fill said column with said magnetic mesh retention means;
and
fine mesh ion exchange particles having a core of magnetic material
encapsulated in an ion exchange resin magnetically attached to and
distributed substantially throughout said retention means, said ion
exchange particles being retained by said retention means in said
column during both operation and regeneration of said ion exchange
particles to provide a fixed-bed ion exchange resin for the ion
exchange treatment of liquids, whereby rapid exchange rates are
achievable in said column without excessive pressure drop.
2. The apparatus of claim 1 wherein said particles have a size of
less than approximately 20 microns.
3. The apparatus of claim 2 wherein said retention means comprise
stainless steel wool.
4. The apparatus of claim 3 wherein said stainless steel wool
occupies 2-5 percent of the total volume of said column.
5. The apparatus of claim 2 wherein said ion exchange resin is an
anion exchange material.
6. The apparatus of claim 2 wherein said ion exchange resin is a
cation exchange material.
7. The apparatus of claim 6 wherein said core is barium
ferrite.
8. The apparatus of claim 1 further including a pump means for
directing the liquid to be treated to said column and means for
introducing a regenerant solution for said ion exchange resin into
said column.
9. A method for the ion exchange treatment of liquids with
fixed-bed ion exchange resins comprising the steps of:
conveying liquid to be treated to the inlet of a column, said
column containing fine mesh ion exchange particles having a core of
magnetic material encapsulated in an ion exchange resin
magnetically attached to and distributed substantially throughout
magnetic mesh retention means which loosely fills said column, said
ion exchange particles being retained by said retention means in
said column during both operation and regeneration of said ion
exchange particles thereby providing a fixed-bed ion exchange resin
for the ion exchange treatment of liquids;
contacting said liquid with said resin particles in said column for
a time sufficient to effect an ion exchange; and
conveying the treated liquid out of the column.
10. The method of claim 9 wherein the liquid to be treated is hard
water, said ion exchange resin is a cation exchange material, and
the treatment involves softening of said hard water to produce soft
water.
11. The method of claim 10 wherein said particles have a size of
less than approximately 20 microns.
12. The method of claim 11 wherein said retention means is a
stainless steel wool.
13. The method of claim 12 wherein said particles are dispersed in
said stainless steel wool by slowly adding said particles to said
column as liquid is pumped through the column at rates of about
18-20 gpm/ft.sup.3.
14. The method of claim 13 wherein said liquid to be treated is
flowed through said column at a rate of less than about 18
gpm/ft.sup.3 and said ion exchange resin is regenerated by
treatment with a regenerant solution at a rate of less than about
18 gpm/ft.sup.3.
Description
BACKGROUND OF THE INVENTION
A current practice by individual, institutional, industrial, and
municipal consumers for the production of soft water is to use
fixed-bed ion exchange resins, usually a sulfonated cation exchange
resin such as a styrene-divinylbenzene copolymer. Hydraulic
considerations currently limit resin particles to a size which
gives maximum capactiy with an acceptable pressure drop at high
flow rates. Most ion exchange resins used currently are generally
sperical in shape and have diameters of 300 to 1000 microns (i.e.,
20-50 mesh, U.S. Standard Screens).
However, the kinetics of 20-50 mesh resins impose limitations on
column design that could be eliminated or at least significantly
moderated by using a finer mesh resin. Fine mesh resins having
diameters of only 15-20 microns (rather than the 300 to 1000 micron
diameter resins now in use) have ion exchange rates on the order of
15 times faster than the conventional larger diameter resins and
more efficient use of the ion exchange capacity. However, they have
not been found acceptable for commercial use in the past because of
hydraulic considerations. In fixed beds, fine mesh ion exchange
resins cause excessive pressure drops, are prone to clogging and
fouling, and are extremely difficult to backwash because they are
easily carried out of the ion exchange column in the backwash
cycle.
For many years the art has attempted to solve these problems so
that advantage could be taken of the faster exchange rates
achievable by using resins with increased surface area. For
example, U.S. Pat. No. 2,460,516 to Luaces suggested that an ion
exchange resin be deposited on the surface of a porous body to
increase the surface area available during water softening.
Voigtman, U.S. Pat. No. 2,798,850, disclosed coating felted or
bat-type fibrous materials such as cellulosics, glass, or asbestos
with various ion exchange resins to increase their exchange
capacity.
Others have encapsulated magnetic particles in ion exchange resins.
Examples of this are Weiss et al., U.S. Pat. Nos. 3,560,378,
Turbeville, 3,657,119, and Weiss et al., 3,890,224. Weiss et al.
3,560,378 recognized the problems that fine ion exchange resins
exhibited such as excessive pressure drop, quick fouling, and loss
through entrainment. Their solution, however, was to use the
encapsulated magnetic resins in an agitated mixer system during
liquid treatment and then to magnetically coalesce the resin
particles after treatment. Weiss et al. 3,560,378 did not purport
to solve the problems associated with fine mesh resins when used in
a fixedbed process. They did compare the reaction kinetics of gamma
iron oxide particles encapsulated with trimethylol phenol N,N
bis(3-amino propylmethylamine) having a particle size range of
250-500 microns with a standard size 350-1200 micron resin in fixed
bed operation and found them to be substantially the same. However,
no data on bed size, flow rates, or pressure drops was
reported.
Svyadoshich et al. in "Wastewater Purification Using
Superparamagnetic Dispersed Ion Exchanger in Constant Magnetic
Field", 10 Soviet Inventions Illustrated 2 (#41 Nov. 1976), used a
column surrounded by an electromagnetic coil which produced a
magnetic field of 350 Oersted and a super-paramagnetic cation
exchange resin (identified only as KU-2-8-f) 40-60 microns in
diameter to obtain ion exchange rates eight times faster than
conventional size resins.
In the field of water purification, attempts have been made to use
high-gradient magnetic fields to separate and extract weakly
paramagnetic submicron particles from fluid streams. DeLatour and
Kolm, "High-Gradient Magnetic Separation: A Water Treatment
Alternative", J. Am. Water Works Assoc. 325-327 (June 1976),
discussed a number of suggestions for separation including possible
use of a matrix of stainless steel wool in a column under the
influence of a magnetic field to capture and hold magnetic
particles from a fluid stream.
However, none of the above-mentioned prior art has satisfactorily
solved the problems associated with fine mesh resins in fixed-bed
columnar operation. Accordingly, the need still exists for
increasing the efficiency of ion exchange processes which use
fixed-bed columnar operation and yet will avoid the problems
associated with fine mesh ion exchange resins when used in such
columns.
SUMMARY OF THE INVENTION
Barium ferrite powder or other suitable ferromagnetic materials
having a particle size of about 2 microns is encapsulated within an
ion exchange resin, yielding a final particle size of less than
approximately 20 microns. The particles are then magnetized and
distributed throughout an ion exchange column loosely filled with a
magnetic mesh retention means such as stainless steel wool where
they are allowed to attach themselves. The column is typically
operated in a down or up flow mode, i.e., the liquid to be treated
is transported to the top or bottom of the column and flows through
the resin attached to the magnetic mesh retention means at rates of
approximately 18 gpm/ft.sup.3 (gallons per minute per cubic foot).
In a preferred form of the invention, the resin is an organic
polymer suitable for use in water softening. Softening is
accomplished by the exchange of monovalent sodium cations on the
resin for divalent cations in the liquid being treated. After
breakthrough capacity is reached, the column is regenerated by
flowing a regenerant solution such as a solution of sodium chloride
at rates of up to about 6 gpm/ft.sup.3 in a direction
countercurrent or cocurrent to that of normal operation. Contact
times of less than 30 minutes are sufficient for resin
regeneration, and the magnetic mesh retention means maintains the
ion exchange particles in the column.
Maintenance of a relatively high void volume throughout the column
keeps pressure drops through the column at acceptable levels. For
example, at flow rates of about 18 gpm/ft.sup.3, only a 9 psi/ft of
column bed drop was observed. For comparison purposes, the pressure
drop in a column using nonmagnetic ion exchange resin of the same
particle size approaches 1000 psi/foot of bed.
Accordingly, it is an object of this invention to enable use of
fine mesh ion exchange particles (i.e., less than approximately 20
micron size) in a columnar mode of operation to obtain the
advantages of rapid exchange rates and more efficient utilization
of resin capacity.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a diagrammatic representation of the ion exchange column
containing magnetic mesh retention means used in the practice of
this invention.
FIG. 2 is a graph comparing pressure drop versus flow rate for
standard size resins and the fine mesh ion exchange particles of
this invention in columnar operation.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The fine mesh ion exchange particles used in the practice of this
invention may be made by methods well known in the art. For
example, magnetic ion exchange resin particles may be prepared
using the methods disclosed by Weiss et al., U.S. Pat. Nos.
3,890,224 and 3,560,378. Although the preferred final particle size
is approximately 15-20 micron, much smaller size resin particles,
as small as 4-5 micron, are operable in the invention. Thickness of
the resin excapsulation over the magnetic core material is not
critical and may vary depending upon the final size of the
particles desired. The magnetic core of the particle may consist of
any suitable ferromagnetic material such as elemental iron, gamma
iron oxide, magnetite, or barium ferrite (BaFe.sub.12 O.sub.19).
Barium ferrite is preferred because it is highly resistant to acids
and bases, is relatively inexpensive, has a high magnetizing force,
and exhibits a high degree of resistance to
self-demagnetization.
Depending on the specific properties desired and the specific type
of ions desired to be removed from (or added to) the liquid to be
treated, a wide variety of both cation and anion exchange resins,
well known in the art, may be used to encapsulate the magnetic core
material. For example, the resins disclosed in Weiss et al., U.S.
Pat. Nos. 3,890,224, 3,560,378, and 3,645,922 may be used. In most
water softening systems, the ions which are removed from the water
are divalent cations such as calcium and magnesium. Thus, in those
systems, it is preferable to use a cation exchange resin such as
styrene divinylbenzene resin or a sulfonated ethylene-vinyl acetate
copolymer cross-linked about 25% with toluene diisocyanate.
After encapsulation, the particles are magnetized by exposing them
to a magnetic field of 10,000 or more Gauss for about 5 minutes. A
preferred method of magnetizing the particles is to slurry them
into a square channel of 12 mm width and 3 mm thickness between
faces of a laboratory magnet with 15.0 cm poles tapered to 5.0 cm
faces. Fine mesh ion exchange particles magnetized in this manner
will remain firmly attached to the magnetic mesh retention means of
the invention at flow rates of up to about 18 gpm/ft.sup.3 in both
the operational and regeneration mode of the column. To distribute
the fine mesh ion exchange particles evenly over the surface of the
magnetic mesh retention means, water is pumped through the column
containing the retention means at high flow rates of about 18-20
gpm/ft.sup.3. The particles are slowly added to the column and are
evenly distributed throughout the column by the flowing water. This
even distribution remains during normal service operational flow
rates of 2-4 gpm/ft.sup.3 and normal regeneration flow rates of 4-5
gpm/ft.sup.3 as well as at the higher flow rates mentioned above.
Although even distribution of the fine mesh ion exchange particles
is preferred, it is not critical to the operation of the
system.
In domestic water softening applications, the preferred magnetic
mesh retention means is stainless steel wool. The stainless steel
wool serves two purposes. It serves as a matrix to which the
magnetic resin particles attach themselves, and it also serves to
provide a tortuous path for the liquid to be treated and fills
extra space in the column. Thus, any fine mesh ion exchange
particles dislodged during operation or regeneration may be
captured by the extra wool downstream. To provide for an acceptably
low pressure drop through the column during operation and yet
provide sufficient area for the magnetic particles to attach,
preferably, the magnetic mesh occupies only 2 to 5 percent of the
total volume in the column. Even after the fine mesh ion exchange
particles have been loaded onto the steel wool, about 80 percent of
the volume in the column remains void space.
For industrial water treatment applications, where corrosive or
acidic media may be encountered, the preferred magnetic mesh
retention means is a material which will resist attack by corrosive
or acidic media. Such mesh retention means may take the form of a
ferromagnetic material such as stainless steel wool coated with an
acid resistant coating or a magnetic material, such as nickel or
nickel alloys, which are more resistant to acid attack or which
have been treated to resist corrosion and acid attack.
Referring now to FIG. 1 which schematically illustrates the
operation of an apparatus of the type which may be used in one
embodiment of the present invention, water to be treated is pumped
(by means not shown) through inlet 32 into pipe 34. During normal
operation, valves 20 and 24 are open while valves 22 and 25 are
closed. The water to be treated enters the top of column 10 and
flows downwardly over the magnetized resin particles 14 attached to
magnetic mesh retention means 12. The magnetic mesh retention means
12 is supported in the column by support 18. After passing through
column 10, the treated water is pumped through pipe 36 to outlet
30. The measure pressure drop in the column for the results
reported in the examples below, the column was attached to a
mercury differential manometer at sampling points 26 and 28. A
commercial embodiment of the column would not have the manometer
hookup.
When the fine mesh ion exchange particles in the column need
regeneration, valves 20 and 24 are closed and valves 22 and 25 are
opened. Regenerant solution, such as a brine (sodium chloride)
solution, is pumped through the column 10 in a direction
countercurrent to normal operation. Optimum regenerating conditions
vary with the particular ion exchange resin used. In water
softening systems, brine concentrations ranging from 8 to 16
percent are generally used. Such concentrations are directly
related to the degree of resin crosslinking. As brine concentration
increases, it causes the resin to shrink thereby inhibiting.
migration of ions into and out of the resin. At lower brine
concentrations, fewer sodium ions are available at any given time
to displace divalent cations such as calcium and magnesium. It has
been found that less concentrated brine solutions contacting the
particles at high regeneration flow rates will yield the best
results. The less concentrated brine solutions are less viscous,
and it has been found that regeneration of the resin is much more
rapid when the regenerant solution is in turbulent flow.
The following examples illustrate the advantages to be attained
through use of the apparatus of the present invention.
EXAMPLE 1--Comparison of pressure drops
Data published by Dow Chemical Company, A Laboratory Manual on Ion
Exchange (1971), on the effects of flow rate (gpm/ft.sup.2) versus
pressure drop (psi/ft of resin bed) in columnar operation for a
300-850 micron and a 150-300 micron sized Dowex styrene
divinylbenzene were compared with pressure drops encountered when
using the apparatus of the present invention. For comparison
purposes, 15-20 micron size particles comprising a barium ferrite
core encapsulated with ethylene-vinyl acetate resin crosslinked
about 25 percent with a toluene diisocyanate adduct were dispersed
in about 0.013 ft.sup.3 of a stainless steel wool mesh in a 20 mm
inside diameter column 400 cm in length. The results of the
comparison are shown in FIG. 2. As can be seen, pressure drops in
columnar operation using the 15-20 micron particle size five mesh
ion exchange particles of the present invention are actually less
than that encountered using 150-300 micron particle size resin and
compare favorably to the even larger 300-850 micron particle size
resin.
EXAMPLE 2--Regeneration contact times
For maximum efficiency in regenerating most commercial ion exchange
resin systems containing 300 to 1000 micron size styrene
divinylbenzene resins, brine contact times (i.e., the length of
time that the brine solution is in contact with the resin) should
be about 50 minutes. Brine contact times of less than 10 minutes
will decrease the operating capacity of the resin about 30 percent,
and if brine contact times are reduced below 5 minutes, capacity
will be decreased over 50 percent. Resin manufacturers recommend
regeneration flow rates of from 0.2 to 1.0 gpm/ft.sup.3, noting
that lower operating capacities will result if flow rates deviate
significantly from this range.
For comparison purposes, the 15-20 micron size fine mesh ion
exchange particles of Example 1 were regenerated using a 10 percent
brine concentration and a brine loading of 4 lbs. NaCl/ft.sup.3.
Results are reported in the table below.
______________________________________ Q.sub.R t.sub.C.sbsb.R
Q.sub.S t.sub.C.sbsb.S X.sub.B.sbsb.T (gpm/ft.sup.3) (min)
(gpm/ft.sup.3) (min) (Kgr/ft.sup.3)
______________________________________ 0.42.sup.a 18.4 1.2 6.6 1.19
0.83.sup.A 9.2 1.2 6.6 1.44 6.43.sup.a 1.2 17.7 0.4 1.72 1.65.sup.b
4.6 1.2 6.6 1.00 6.4.sup.b,1 1.2 1.2 6.6 1.58
______________________________________ .sup.a brine loading = 4 lbs
NaCl/ft.sup.3 .sup.b brine loading = 8 lbs NaCl/ft.sup.3 .sup.1 20%
brine, all others at 10% LEGEND: Q.sub.R - Regen Flow Rate
t.sub.C.sbsb.R - Regen Contact Time Q.sub.S - Service Flow Rate
t.sub.C.sbsb.S - Service Contact Time X.sub.B.sbsb.T - Breakthrough
Capacity 17 mg/l (1.0 grain/gallon)
As can be seen, for the particular fine mesh ion exchange particles
used, regeneration flow rates above 6 gpm/ft.sup.3 and brine
contact times of as little as 1.2 min. yield significant increases
in the operating capacity of the ion exchange particles. In fact,
these data show that the greater the regeneration flow rate (within
limits), the greater the increase in operating capacity (as shown
by increased breakthrough capacity), and at brine contact times far
less than those recommended for prior art systems.
EXAMPLE 3--Service cycle contact times
With bed depths of 30 inches or more, capacities obtained with
conventionally sized ion exchange particle systems are decreased
about 10 percent when service flow rates reach 10 gpm/ft.sup.3
(contact time of about 2 minutes) and fall significantly with
increasing flow. Decreasing bed depth while maintaining a constant
flow rate has essentially the same effect. Thus, for most
commercial systems, service flow rates in the range of 2 to 5
gpm/ft.sup.3 (contact times of 7.5 to 3.75 minutes) are
recommended.
Again, using the fine mesh ion exchange particles of Example 1 for
comparison purposes, service cycle flow rates of from 1.2 to 17.7
gpm/ft.sup.3 with corresponding contact times of 6.6 minutes to 25
seconds were run. As can be seen from the results reported in the
table in Example 2, for the particular resin used, service flow
rates far in excess of prior art systems were possible without
decreasing the operating capacity of the system.
It is postulated that because of the extremely small particle size
of the ion exchange particles used in the present invention, film
diffusion (i.e., the diffusion of ions through the film of solution
surrounding each particle) is the rate determining factor for the
system used in the practice of this invention while for many prior
art systems, particle diffusion (i.e., the diffusion of ions
throughout a particle) is the rate determining factor. The above
data bear this out because high flow rates serve to decrease the
film thickness surrounding a given particle which increases the
rate of exchange of film diffusion controlled systems. That is why
high flow rates are advantageous to the system utilized in the
practice of this invention.
As can be seen from the above examples, fine mesh ion exchange
particles, i.e., less than approximately 20 micron particle size,
can be used in the apparatus of the present invention with
acceptable pressure drops during columnar operation while obtaining
the rapid exchange benefits of the fine mesh ion exchange
particles. Prior art plugging and fouling problems are avoided
while the efficiency of the ion exchange process in water softening
systems has been increased.
While the apparatus and methods herein described constitute
preferred embodiments of the invention, it is to be understood that
the invention is not limited to these precise methods or apparatus,
and that changes may be made in either without departing from the
scope of the invention, which is defined in the appended
claims.
* * * * *